1. Field of the Invention
This invention relates to screen printing, cylinder presses and more particularly, to drive mechanisms for driving a screen printing cylinder press.
2. Description of The Prior Art
U.S. Pat. No. 3,915,088 discloses a commonly-used drive for such screen printing, cylinder presses. This drive includes a rotating crank mechanism which is driven by a motor with the crank mechanism providing a drive for a lever subassembly, which turns a gear segment to rotate a gear connected to the cylinder A screen printing carriage has a rack which is driven by the gear on the cylinder to reciprocate the carriage with oscillation of the cylinder. A particular problem with the crank drive is that it provides a harmonic motion with a substantially equal percentage of the time being used for acceleration of the cylinder and screen printing carriage and for the deceleration thereof prior to reversing the direction of travel of the cylinder and screen printing carriage To change the direction of cylinder rotation and carriage travel requires overcoming considerable inertia. When this inertia is not smoothly overcome, there may be a banging or other hitting as the cylinder reverses its direction of rotation which may cause the screen not to be properly registered with respect to a prior image or to specific spot on the web.
With a crank as in U.S. Pat. No. 3,915,088 or with a conventional cam used to drive a cylinder or web press, little has been accomplished in controlling the inertia of the cylinder and the time period for deceleration of the cylinder and the traveling printing screen carriage.
The present invention is directed to providing lower inertia and a greater time period for slowing down and stopping the travel of the cylinder and screen printing carriage in cylinder presses.
To these ends, the present invention is directed to providing a controlled inertia with a profiled cam drive for cylinder screen printing presses in which the inertia is calculated and is controlled by minimizing the velocity, particularly when stopping the movement of the cylinder and screen printing carriage in one direction and just prior to reversing their directions of travel in the opposite directions. This is achieved by providing a faster acceleration from a stopped position over a shorter period of time than with a crank and then, providing for a much longer time and a much slower movement than with a crank, resulting in a reduced inertia for the travel of the cylinder and printing carriage when they are nearing the end of their travel in one direction.
U.S. Pat. No. 3,915,088 discloses an adjustable stroke mechanism whereby the length of the stroke provided by the drive may be easily adjusted to change the amount of rotary movement of cylinder. However, such adjustment is rather cumbersome. The present invention provides an improved stroke adjustment mechanism for cylinder presses.
Accordingly, a general object of the present invention is to provide a new and improved drive for cylinder screen printing presses.
Another and more specific object of the invention is to provide an improved drive having improved inertia and displacement characteristics relative to the harmonic accelerations and decelerations from a crank drive.
Another object of the invention is to provide the drive mechanism with a new and improved stroke adjustment mechanism for cylinder screen printing presses.